Storage library systems are used for storage and retrieval of data stored on cartridges. A storage library system may include multiple tape drives, and a robotically-movable hand assembly including a gripper for grasping and removing ejected cartridges from the various tape drives.
Certain tape drives eject cartridges to specific distances and are sensitive to push-back forces or push-back distances. If the ejected cartridge is pushed back into the tape drive with a certain force or to a certain distance, the tape drive will reload the cartridge. Accordingly, this reloading may occur if a movable hand assembly bumps against an ejected cartridge or pushes the cartridge too far into the tape drive prior to grasping the cartridge for removal. Speed is a critical feature of storage library systems, however, in this situation, a substantial time delay is caused because the cartridge must again be ejected from the tape drive for retrieval of the cartridge.
Bumping of the cartridge by the gripper of the hand assembly may occur if the hand assembly is not in the proper vertical position or not in the proper horizontal position for grasping the cartridge. The hand assembly is typically at the end of a multi-arm structure, therefore tolerance stack-up of the various arms may cause the end of the hand assembly to be out of position.
Some tape drives use mechanical hooks to hold the tape cartridge in the proper position in case the hand assembly bumps against the cartridge or attempts to push the cartridge in too far prior to removal. These mechanical hooks add a certain cost and reliability penalty to the storage library system.
Some prior art systems use servo position controllers to limit the movement of the hand assembly. This substantially slows the performance of the library and requires very narrow manufacturing tolerances between the drive and gripping device in order to operate properly.
Therefore, it is desirable to provide an inexpensive and accurate method and apparatus for properly positioning a hand assembly with the respect to a tape drive in order to retrieve an ejected cartridge from a tape drive without forcing the cartridge too far into the tape drive.